package com.hd.trans.utils;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class FileMd5 {

    /**
     * 默认的密码字符串组合，用来将字节转换成 16 进制表示的字符,apache校验下载的文件的正确性用的就是默认的这个组合
     */
    protected static char hexDigits[] = { '0' , '1' , '2' , '3' , '4' , '5' , '6' ,
            '7' , '8' , '9' , 'a' , 'b' , 'c' , 'd' , 'e' , 'f' };

    protected static MessageDigest messagedigest = null ;
    static {
        try {
            messagedigest = MessageDigest.getInstance("MD5" );
        } catch (NoSuchAlgorithmException nsaex) {
            System.err.println(FileMd5.class .getName()
                    + "初始化失败，MessageDigest不支持MD5Util。" );
            nsaex.printStackTrace();
        }
    }

    /**
     * 生成字符串的md5校验值
     *
     * @param s
     * @return
     */
    public static String getMD5String(String s) {
        return getMD5String(s.getBytes());
    }

    /**
     * 判断字符串的md5校验码是否与一个已知的md5码相匹配
     *
     * @param password 要校验的字符串
     * @param md5PwdStr 已知的md5校验码
     * @return
     */
    public static boolean checkPassword(String password, String md5PwdStr) {
        String s = getMD5String(password);
        return s.equals(md5PwdStr);
    }

    /**
     * 生成文件的md5校验值
     *
     * @param file
     * @return
     * @throws IOException
     */
    public static String getFileMD5String(File file) throws IOException {
        InputStream fis;
        fis = new FileInputStream(file);
        byte [] buffer = new byte [ 1024 ];
        int numRead = 0 ;
        while ((numRead = fis.read(buffer)) > 0 ) {
            messagedigest.update(buffer, 0 , numRead);
        }
        fis.close();
        return bufferToHex(messagedigest.digest());
    }


    public static String getMD5String( byte [] bytes) {
        messagedigest.update(bytes);
        return bufferToHex(messagedigest.digest());
    }

    private static String bufferToHex( byte bytes[]) {
        return bufferToHex(bytes, 0 , bytes.length);
    }

    private static String bufferToHex( byte bytes[], int m, int n) {
        StringBuffer stringbuffer = new StringBuffer( 2 * n);
        int k = m + n;
        for ( int l = m; l < k; l++) {
            appendHexPair(bytes[l], stringbuffer);
        }
        return stringbuffer.toString();
    }

    private static void appendHexPair( byte bt, StringBuffer stringbuffer) {
        char c0 = hexDigits[(bt & 0xf0 ) >> 4 ]; // 取字节中高 4 位的数字转换, >>> 为逻辑右移，将符号位一起右移,此处未发现两种符号有何不同
        char c1 = hexDigits[bt & 0xf ]; // 取字节中低 4 位的数字转换
        stringbuffer.append(c0);
        stringbuffer.append(c1);
    }

    public static void main(String[] args) throws IOException {
        long begin = System.currentTimeMillis();

        File file = new File( "C:/12345.txt" );
        String md5 = getFileMD5String(file);

// String md5 = getMD5String("a");

        long end = System.currentTimeMillis();
        System.out.println("md5:" + md5 + " time:" + ((end - begin) / 1000 ) + "s" );
    }
}
